SAM7S256_14 Datasheet, PDF (321/775 Pages) ATMEL Corporation – ARM-based Flash MCU

TWD and TWCK pins may be multiplexed with PIO lines. To enable the TWI, the programmer must perform the fol-
lowing steps:
• Program the PIO controller to:
– Dedicate TWD and TWCK as peripheral lines.
– Define TWD and TWCK as open-drain.
30.5.2 Power Management
• Enable the peripheral clock.
The TWI interface may be clocked through the Power Management Controller (PMC), thus the programmer must
first configure the PMC to enable the TWI clock.
30.5.3 Interrupt
The TWI interface has an interrupt line connected to the Advanced Interrupt Controller (AIC). In order to handle
interrupts, the AIC must be programmed before configuring the TWI.
30.6 Functional Description
30.6.1 Transfer Format
The data put on the TWD line must be 8 bits long. Data is transferred MSB first; each byte must be followed by an
acknowledgement. The number of bytes per transfer is unlimited (see Figure 30-4).
Each transfer begins with a START condition and terminates with a STOP condition (see Figure 30-3).
• A high-to-low transition on the TWD line while TWCK is high defines the START condition.
• A low-to-high transition on the TWD line while TWCK is high defines a STOP condition.
Figure 30-3. START and STOP Conditions
TWD
TWCK
Start
Stop
Figure 30-4. Transfer Format
TWD
TWCK
Start Address R/W Ack
30.6.2 Modes of Operation
The TWI has six modes of operations:
• Master transmitter mode
• Master receiver mode
• Multi-master transmitter mode
Data
Ack
Data
Ack Stop
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
321